ASP.NET MVC 3 JSONP: Does this work with JsonValue

问题:

Phil Haack has an excellent blog post on how to use JSON, data binding, and data validation.

Enter the browser's "same origin policy security restriction." and JSONP where you use $.getJSON() to retrieve the content.

Is there a built in MVC 3 way to do this, or do I need to follow the advice of posts like this? Can you post content? I ask because my colleague implemented a JsonPfilterAttribute among other things to make this work. It's obviously preferred to avoid that if something already exists in MVC 3.

Edit:

Summary: everything works with the exception of accessing a POST variable, i.e., how do I access the POST variable in the context? (comment marking it in the last section of code)

I elected to use this format to call the server:

$.ajax({
    type: "GET",
    url: "GetMyDataJSONP",
    data: {},
    contentType: "application/json; charset=utf-8",
    dataType: "jsonp",
    jsonpCallback: "randomFunctionName"
});

Which produces this response:

randomFunctionName([{"firstField":"111","secondField":"222"}]);

And all this works very well if I use a GET. However, I still cannot get this to work as a POST. Here's the original code posted by Nathan Bridgewater here. This line doesn't find the POST data:

context.HttpContext.Request["callback"];

Either I should be accessing Form in some way, or the MVC data validators are stripping out the POST variables.

How should context.HttpContext.Request["callback"]; be written to access the POST variable or is MVC stripping out these values for some reason?

namespace System.Web.Mvc
{   public class JsonpResult : ActionResult
    {   public JsonpResult() {}

        public Encoding ContentEncoding { get; set; }
        public string ContentType { get; set; }
        public object Data { get; set; }
        public string JsonCallback { get; set; }

        public override void ExecuteResult(ControllerContext context)
        {   if (context == null)
               throw new ArgumentNullException("context");

            this.JsonCallback = context.HttpContext.Request["jsoncallback"];

            // This is the line I need to alter to find the form variable:

            if (string.IsNullOrEmpty(this.JsonCallback))
                this.JsonCallback = context.HttpContext.Request["callback"];

            if (string.IsNullOrEmpty(this.JsonCallback))
                throw new ArgumentNullException(
                    "JsonCallback required for JSONP response.");

            HttpResponseBase response = context.HttpContext.Response;

            if (!String.IsNullOrEmpty(ContentType))
               response.ContentType = ContentType;
            else
               response.ContentType = "application/json; charset=utf-8";

            if (ContentEncoding != null)
                response.ContentEncoding = ContentEncoding;

            if (Data != null)
            {   JavaScriptSerializer serializer = new JavaScriptSerializer();
                response.Write(string.Format("{0}({1});", this.JsonCallback,
                    serializer.Serialize(Data)));
    }   }   }

    //extension methods for the controller to allow jsonp.
    public static class ContollerExtensions
    {
        public static JsonpResult Jsonp(this Controller controller, 
               object data)
        {
            JsonpResult result = new JsonpResult();
            result.Data = data;
            result.ExecuteResult(controller.ControllerContext);
            return result;
        }
    }
}

回答1:

As far as receiving a JSON string and binding it to a model is concerned the JsonValueProviderFactory does this job out of the box in ASP.NET MVC 3. But there is nothing built-in for outputting JSONP. You could write a custom JsonpResult:

public class JsonpResult : JsonResult
{
    public override void ExecuteResult(ControllerContext context)
    {
        if (context == null)
        {
            throw new ArgumentNullException("context");
        }
        var request = context.HttpContext.Request;
        var response = context.HttpContext.Response;
        string jsoncallback = (context.RouteData.Values["jsoncallback"] as string) ?? request["jsoncallback"];
        if (!string.IsNullOrEmpty(jsoncallback))
        {
            if (string.IsNullOrEmpty(base.ContentType))
            {
                base.ContentType = "application/x-javascript";
            }
            response.Write(string.Format("{0}(", jsoncallback));
        }
        base.ExecuteResult(context);
        if (!string.IsNullOrEmpty(jsoncallback))
        {
            response.Write(")");
        }
    }
}

And then in your controller action:

public ActionResult Foo()
{
    return new JsonpResult
    {
        Data = new { Prop1 = "value1", Prop2 = "value2" },
        JsonRequestBehavior = JsonRequestBehavior.AllowGet
    };
}

which could be consumed from another domain with $.getJSON():

$.getJSON('http://domain.com/home/foo?jsoncallback=?', function(data) {
    alert(data.Prop1);
});